(a) Field of the Invention
The present invention relates to a process for preparing alkyl glycosides, and more particularly to a process for preparing pale-colored and transparent alkyl glycosides.
(b) Description of the Related Art
Alkyl glycosides are non-ionic surfactants made from natural materials, which provide detergency, foaming, emulsifying, and wetting properties comparable to those of other non-ionic surfactants. Alkyl glycosides have an advantage of reducing water pollution as applied to detergents since they have a superior biodegradability, and also because of their hypo-allergenic property they are suitable for decreasing allergic reactions of skin commonly associated with the detergents.
Conventionally, alkyl glycosides are prepared by a method of reacting carbohydrates with low fatty alcohol such as butyl alcohol in presence of an acid catalyst such as sulfuric acid or hydrochloric acid, and then reacting carbohydrates with high fatty alcohol as disclosed in German Patent Application No. 3 723 826 A1; German Patent Application No. 3 827 534 A1; German Patent Application No. 3 842 541 A1; EPO Publication No. 0 306 650 A1; EPO Publication No. 0 306 651 A1 and EPO Publication No. 0 306 652 A1. Because the method utilizes two reacting steps having a long reaction time, the process becomes complex. Additionally, there is a drawback in that the high fatty alcohol and low fatty alcohol must be stored separately, further complicating the method.
To solve the above problems, EPO Publication No. 0 387 913 A1 and EPO Publication No. 0 388 857 A1 describe a process of reacting carbohydrate such as glucose with high fatty alcohol in presence of an acid catalyst. This method has a problem in that removing an excess of unreacted high fatty alcohol cause brown color to develop. In the neutralization step, an alkaline substance is added to remove remaining acids from the reaction, in order to prevent the alkyl glycosides from reversibly decomposing into glucose and alcohol at a high temperature. However, in the above neutralization step, an exact neutralization point is difficult to obtain, and consequently adding an alkaline substance in excess is not an uncommon problem. An excess of alkaline substance in the above step cause brown color to develop, also attributed by the presence of carbohydrates, oxygen, high temperature, alkali, proteins, metal ions, minerals or vitamins.
To solve the above problem, U.S. Pat. No. 4,950,743; EPO Publication No. 0 362 671 A1; EPO Publication No. 0 389 753 A1; German Patent Application No. 3 940 827 A1 and German Patent Application No. 4 019 175 A1 describe a method of bleaching alkyl glycosides with peroxide such as hydrogen peroxide or ozone (O3), and stabilizing with sodium borohydride (NaBH4). This method has problems in that it provides an unsatisfied degree of color (closest to transparency), and color reversion may occur during storage of surfactants.
PCT Publication No. WO 94/02494; PCT Publication No. 94/24139 and PCT Publication No. 95/23169 describe methods utilizing a neutralizing agent having a weak alkaline substance such as a mixture of sodium hydroxide and magnesium oxide in order to decrease the color reversion. Again, these methods fall short of solving the above problem of removing brown coloration while obtaining a satisfactory degree of color closest to transparency.
Additionally, in the conventional methods, there is a further drawback in that the removed fatty alcohol, still having brown coloration, cannot be utilized again until it is refined in a distillation process and have its color removed. This additional step complicates and adds cost to the manufacturing process.
It is an object of the present invention to provide a process for preparing pale-colored and transparent alkyl glycosides.
Another object is to provide a process of collecting excess fatty alcohol without a refining step.
To achieve the above objects the present invention provides a process for preparing pale-colored and transparent alkyl glycosides by reacting a glucose with a high fatty alcohol in presence of an acid catalyst, comprising the steps of admixing, reacting, neutralizing, distilling, diluting and bleaching. In the above process, the reacting step is controlled by a product""s color and an amount of unreacted glucose; the neutralizing step is controlled by alkali metal oxide powders and the product""s color; the distilling step is controlled by an unreacted fatty alcohol; and the diluting step is controlled by refined ion water and sealed vessel without oxygen.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The object and advantage of the invention may be realized and attained by means of the instrumentality and combinations particular pointed out in the appended claims.
The preferred processes according to the present invention will now be described in detail.
A first preferred process for preparing pale-colored and transparent alkyl glycosides according to the present invention comprises the steps of:
1) admixing a carbohydrate such as glucose with high fatty alcohol having 8 to 22 carbon atoms;
2) reacting the mixture in presence of an acid catalyst such as p-toluene sulfonic acid (p-TSA) at a high temperature under a high vacuum condition until the reaction product""s color is between ochre and wormwood and the amount of unreacted glucose is less than 3% of the reactants"" weight;
3) neutralizing the reaction product having water content of less than 1000 ppm by adding neutralizing agent such as alkali metal oxide powders that have a specific surface area of more than 30 m2/g, and stirring until the reaction product""s color is yellow and the reaction product pH is 7.0xcx9c8.0;
4) distilling the neutralized reaction product to remove the unreacted residual fatty alcohol at a high temperature under a high vacuum condition until the amount of the unreacted fatty alcohol is less than 2% of the distilled reaction product""s weight;
5) diluting the distilled reaction product by adding refined ion water having pH of 2.0xcx9c6.0, in a vessel sealed and charged with nitrogen gas; then
6) bleaching the diluted reaction product with a small amount of bleaching agent such as hydrogen peroxide.
In the above steps, it is preferable that the amount of fatty alcohol in step 1) is 3xcx9c5 mole per mole of glucose; the amount of acid catalyst in step 2) is 0.002xcx9c0.007 mole per mole of glucose; the reaction temperature is 110xcx9c125xc2x0 C.; the reaction pressure is 16xcx9c20 torr; and the reaction time is 80xcx9c200 minutes.
The preferred alkali metal oxide of the neutralizing agent in step 3) is magnesium oxide, aluminum oxide, calcium oxide, zinc oxide or their mixture and the amount used is between 0.5 mole and 1.0 mole based on the acid catalyst used. The stirring temperature is between 85xc2x0 C. and 105xc2x0 C., and the stirring time is between 20 minutes and 40 minutes.
It is also preferable that the distillation instrument in step 4) is a thin film evaporator, and that the color of the diluted reaction product in step 5) is yellow having between 4 and 11 Gardner number.
The preferred vessel in step 5) have an outlet operated automatically by a level sensor or a pressure sensor and the dilute concentration is between 40% and 60%. Also a residue of the bleaching agent in step 6) may be decreased from the reaction product by a heat exchanger.
A second preferred process according to the present invention will now be described below.
1) reacting glucose and high fatty alcohol of having 8 to 22 carbon atoms, in presence of an acid catalyst until the amount of unreacted glucose in reaction product is less than 3% of the distilled reactant product"" weight;
2) neutralizing the reaction product by adding magnesium oxide powders having a specific surface area of more than 50 m2/g, preferably more than 80 m2/g, at 85xcx9c105xc2x0 C. temperature for 20xcx9c40 minutes;
3) distilling the neutralized reaction product until the amount of the unreacted residual fatty alcohol is less than 2% of the reactants"" weight;
4) diluting the distilled reaction product; then
5) bleaching the diluted reaction product with hydrogen peroxide.
In the above process, it is preferable that the acid catalyst is para-toluene sulfonic acid in the reacting step and that the amount of magnesium oxide used is between 0.5 mole and 1.0 mole, based on the acid catalyst used.
A third preferred process according to the present invention will be described below.
1) reacting glucose and high fatty alcohol of having 8 to 22 carbon atoms in presence of an acid catalyst until the amount of unreacted glucose in reaction product is less than 3% of the reactants"" weight;
2) neutralizing the reaction product having water content of less than 1000 ppm, preferably less than 500 ppm, by adding alkali metal oxide powders such as magnesium oxide, aluminum oxide, calcium oxide, zinc oxide or their mixture having a specific surface area of more than 30 m2/g, preferably more than 50 m2/g.
In the above process, it is preferable that the amount of alkali metal oxide used is between 0.5 mole and 1.0 mole, based on the acid catalyst used, and that the neutralization is carried out by stirring for 20xcx9c60 minutes at 85xcx9c105xc2x0 C. temperature until the pH of the neutralized reaction product is between 7.0 and 8.0.
A fourth preferred process according to the present invention will be described below.
1) reacting glucose and high fatty alcohol in presence of an acid catalyst;
2) neutralizing the reaction product by adding neutralizing agent until the reaction product"" pH is 7.0xcx9c8.0;
3) distilling the neutralized reaction product; then
4) diluting the distilled reaction product by adding refined ion water having pH 2.0xcx9c6.0, preferably pH of 3.0xcx9c5.0, in a vessel sealed and charged with nitrogen gas.
In the above process, it is preferable that the vessel has an outlet operated automatically by a level sensor or a pressure sensor.
A fifth preferred process according to the present invention will be described below.
1) admixing a carbohydrate such as glucose with high fatty alcohol having 8 to 22 carbon atoms;
2) reacting the mixture in presence of an acid catalyst until the reaction product""s color is between ochre and wormwood and the amount of unreacted glucose is less than 3% of the reactants"" weight;
3) neutralizing the reaction product by adding magnesium oxide powders, and stirring until the reaction product""s color is yellow;
4) distilling the neutralized reaction product until the amount of the unreacted residual fatty alcohol is less than 2% of the distilled reaction product""s weight;
5) diluting the distilled reaction product; then
6) bleaching the diluted reaction product with hydrogen peroxide.
In the above steps, it is preferable that the neutralization is carried out by stirring for 20xcx9c60 minutes at 85xcx9c105xc2x0 C.
In accordance with the present invention, factors that affect color quality and cleaning effect of detergents are described below.
The first factor is a length of carbon chain that a fatty alcohol contains. Generally, alkyl glycosides made from a fatty alcohol containing less than 10 carbon atoms have a superior degree of color, and they are very hydrophilic that they may be soluble in water. However, alkyl glycosides made from a fatty alcohol containing more than 12 carbon atoms have an inferior degree of color, and they are very hydrophobic that they are suitable as emulsifying agent or wetting agent. Accordingly, a mixture of both the high and low number carbon chain fatty alcohol is employed as raw materials for a detergent having a superior degree of color and a cleaning effect.
The second factor is a mole ratio of fatty alcohol to glucose. For example, if the mole ratio of fatty alcohol and glucose (A/G) is over 5, the product may have a good degree of color that may be found at the end point of reaction without difficulty. However, the product has an inferior cleaning effect because of it""s a low degree of oligomerization. On the other hand, if the mole ratio is below 2 or 3, the product may have an inferior degree of color. Hence, it is preferable that the reaction mole ratio of fatty alcohol to glucose is between 3 to 5 to obtain alkyl glycosides having a superior degree of color and cleaning effect.
The third factor is an oxygenation of reaction product produced at a temperature above 130xc2x0 C. while removing excess fatty alcohol. The oxygenation provides final product having an inferior degree of color.
The fourth factor is a neutralizing condition such as pH. In the neutralizing step it is difficult to control pH with a neutralizing agent. If the neutralization is not sufficient, the reaction may be reversed and alkyl glycosides may decompose to glucose and alcohol, and the isolated glucose becomes a caramel. If the neutralization is excessive, the product may become an alkaline substance and brown coloration may develop. Hence, it is preferable that pH is maintained in a range of 7.0 to 8.0. The temperature and the time required in the neutralizing step also influence pH and color quality.
Accordingly, it is preferable that in the admixing step the amount of fatty alcohol is 3xcx9c5 mole per mole of glucose; that in the reacting step the amount of acid catalyst is 0.002xcx9c0.007 mole per mole of glucose; the reaction temperature is 110xcx9c125xc2x0 C.; the reaction vacuum pressure is 16xcx9c20 torr; the reaction time is 80xcx9c200 minutes; and the amount of unreacted glucose is below 3% of the reactants"" weight.
In the neutralizing step of the present invention, a neutralizing agent employed is alkali metal oxide powders such as magnesium oxide, aluminum oxide, calcium oxide, zinc oxide in an amount between 0.5 mole and 1.0 mole, based on the amount of acid catalyst used, on a molar basis. The stirring temperature range is from 85xc2x0 C. to 105xc2x0 C.; stirring time is between 20 minute to 40 minute; neutralizing end point range is from pH of 7.0 to 8.0.
In distilling step of the present invention, the reaction product distilled by heat should have an unreacted fatty alcohol below 2% of the distilled reaction product""s weight. And it is desirable to cool the distilled reaction product quickly until the product temperature reaches below 130xc2x0 C. for obtaining a superior degree of color. And the collection of the distilled excess fatty alcohol can be recycled without the refining step.
In the diluting step of the present invention, the controlled reaction product color is yellow having Gardner number range of from 4 to 11.
In the bleaching step of the present invention, after removing the residue of the bleaching agent by a heat exchanger, the product obtained is pale and transparent color.
The following examples illustrate the advantages of the present invention.